This invention relates to the production of drilling fluids for oil and gas exploration and production operations. Specifically, the present invention relates to the sulfonation of uintaite and the application of sulfonated uintaite to oil and gas well drilling fluids, oil and gas well completion fluids, and fluid loss control of hydraulic fracturing fluids for oil and gas wells.
It is well known that in penetrating the earthen formations to tap subterranean deposits, such as gas or oil, that penetration is accomplished by well drilling tools and a drilling fluid. Drilling fluid, also commonly known as drilling mud, serves to cool and lubricate the drill bits, to carry the cuttings to the surface as the drilling fluid is circulated in and out of the well, to support at least part of the weight of the drill pipe and drill bit, to provide a hydrostatic pressure head to prevent caving of the walls of the well bore, to deposit on the surface of the well bore a filter cake which acts as a thin, semi-impervious layer to prevent undue passage therethrough of drilling fluids, and to perform other functions as are well known in the drilling art. These fluids must be capable of exhibiting some rather sophisticated performance characteristics such as inhibiting the disintegration of drill cuttings, protecting and/or stopping the sloughing of unstable hard and brittle shales, have lubricating characteristics, reducing fluid loss, and particularly reducing high temperature fluid losses of drilling fluids, and reducing the fluid losses and spurt losses of hydraulic fracturing fluids during the hydraulic fracturing process. Furthermore, the prepared fluids must exhibit a viscosity in both brine waters and fresh waters and in selected oils sufficiently low to allow pumping.
It is also important that the drilling fluid exhibit a relatively low rate of filtration or fluid loss. That is, the drilling fluid should permit little, if any, loss of its liquid phase to the formation penetrated, as is well known to those skilled in the art. Most drilling fluids contain additives and conditioning agents which are important in determining the fluid loss properties of the drilling fluid, as well as inhibiting shale and clay disintegration.
In addition to exhibiting a low rate of fluid loss, it is desirable for the fluid to have certain rheological properties, such as low viscosity and gel strength.
One material known to be effective in drilling fluid is sulfonated asphalt. Sulfonated asphalt marketed under the trademark xe2x80x9cSoltex(copyright)xe2x80x9d by Phillips Petroleum Company has been used as a drilling fluid for many years. Six patents assigned to Phillips Petroleum Company relating to the production of sulfonated asphalt are: Stratton, et al., U.S. Pat. No. 3,028,333; Stratton, et al., U.S. Pat. No. 3,089,842; Pitchford, et al., U.S. Pat. No. 3,089,846; Peacock, et al., U.S. Pat. No. 3,215,628; and, Clampitt, et al., U.S. Pat. No. 4,514,308, incorporated herein by reference. Although sulfonated asphalt has many desirable properties, there still remains a need for a more effective product.
Known problems exist when sulfonating asphalt in the process of production of drilling fluids. A main problem resides with the characteristics of asphalt itself. The softening point of typical conventional refinery asphalts is approximately 130xc2x0 to 155xc2x0 F. In the production of sulfonated asphalt, the drying temperature is higher, 190xc2x0 to 400xc2x0 F., thus causing the non-sulfonated asphalt to be very sticky in the production equipment. In order to avoid this, the drying time must be extended at lower temperatures, resulting in a slow rate of drying. Longer drying times mean lower throughput in the manufacturing process. Moreover, the minimum level of sulfonation of the asphalt is dictated by properties required for smooth mechanical operations during the drying process If the level of sulfonation is too low, the product remains xe2x80x9cgummyxe2x80x9d and sticks to metal surfaces in rotary type dryers at the above temperatures to an extent that makes the process mechanically unworkable. When mechanical rotary dryers are used, the production rate is very much limited to low levels of sulfonation when using asphalts from conventional rude oil type refineries. Also, asphalt must be transported in heated trucks causing difficult handling, storage and heat maintenance problems. A need, therefore, exists for a material which can be efficiently produced at advantageous levels of sulfonation also manufactured without sticking to the production equipment and transported without heating.
Uintaite is a naturally occurring hydrocarbon mineral that was discovered in the early 1860""s in the Uintah Basin in northeastern Utah. It occurs in vertical veins outcropping on the surface and extends downward hundreds of feet. The vertical veins are usually two to six feet wide, and veins as wide as 13 to 20 feet have been discovered and mined. The veins are nearly parallel to each other and are oriented in a northwest to southeast direction. They extend many miles in length and are as deep as 1500 to 2000 feet. Uintaite is mined with modern equipment such as with pneumatic chipping hammers and with mechanical and air hoists. Samuel H. Gibson began to promote the use of uintaite in the mid-1880s as a waterproof coating material for wooden pilings, and as insulation for wire cable and as a unique varnish.
Uintaite is a natural product whose chemical and physical properties vary and depend strongly on the uintaite source. Although uintaite is sometimes loosely described as an asphaltic material, its composition varies greatly from asphalt derived from refining operations. Uintaite is known to have the following characteristics: (1) high asphaltene content; (2) high solubility in organic solvents; (3) high purity and consistent properties; (4) high molecular weight; and, (5) high nitrogen content. One typical general analysis of uintaite shows the following weight percentages: Carbon 84.9%, Hydrogen 10.0%, Nitrogen 3.3%, Sulfur 0.3%, Oxygen 1.4%, Trace Elements 0.1%. Uintaite has a molecular weight of about 3000 which is considered very high compared to asphalt products from conventional crude oil refineries.
Uintaite is also commonly called xe2x80x9cgilsonitexe2x80x9d although this term is believed to be a registered trademark of American Gilsonite Company, Salt Lake City, Utah (Reg. No. 0144,545). Three different companies in the US mine and sell today the naturally occurring mineral uintaite in the form of several softening point ranges. Upon information and belief, all three companies advertise their products as Gilsonite. These three companies are American Gilsonite Company with a corporate address of 109 Stevenson Street, Third Floor; San Francisco, Calif. 94105; LEXCO, INC.; P.O. Box 1198 of Vernal, Utah 84078; and the Ziegler Chemical and Mineral Corporation of 600 Prospect Avenue, Piscataway, N.J. 08854.
Typical uintaite used in drilling fluids is mined from an area around Bonanza, Utah and has a specific gravity of 1.05 with a softening point ranging from 325 deg. F to as high as 400+ deg. F. The lowest softening point material is used less frequently in drilling fluids. Uintaite has a low acid value, a zero iodine number, and is soluble or partially soluble in aromatic and aliphatic hydrocarbons, respectively. It is generally processed and ground to where 99% passes through a 65-mesh Tyler screen with approximately 3% being retained on a 100-mesh screen and 16% on a 200-mesh screen, non-cumulative. Uintaite is very friable so size reduction is easy with minimum equipment required.
American Gilsonite Company sells a variety of Gilsonite resins, sometimes identified by their softening points (Ring and Ball, an ASTM Method). For example, general purpose (GP) uintaite brand resin has a softening point of about 350 deg. F, and uintaite HM has a softening point of about 380 deg. F, and uintaite Select 300 and Select 325 which have softening points of 300 and 325 deg. F, respectively. The softening points of these naturally derived uintaites depend primarily on the source vein that is being mined when the mineral is produced.
Uintaite products are approved by the U.S. Food and Drug Administration for use in resinous and polymeric coatings that come into direct contact with food. Gilsonite falls under xc2xa7 175.300 of the U.S. Food and Drug Administration regulations, Part 3, Subpart (IV), which lists Gilsonite as one of several approved natural resins. Gilsonite in its unaltered state is reported to be non-carcinogenic, non-mutagenic, and non-toxic by recognized test procedures.
Uintaite is described in the Kirk-Othmer Encyclopedia of Chemical Technology, 3rd Ed. Vol. 11, 1986, pp. 802-806; which is incorporated herein by reference. Gilsonite is described in Hawley""s Condensed Chemical Dictionary, Thirteenth Edition, Copyright 1997 by John Wiley and Sons, Inc., p. 537, also incorporated herein by reference.
Uintaite is known to have use in both water-based and oil-based drilling fluids as additives assisting in borehole drilling, and has been believed to reduce the problems found in drilling through troublesome shales. Borehole instability problems are often referred to as sloughing, heaving, spalling or overpressured shales. Some shales hydrate and swell. Others are very hard, brittle, and are fractured.
However, known problems encountered with the use of uintaite as a drilling fluid are that it does not water wet with most surfactants and cannot be dispersed in water. Thus, stable dispersions of uintaite are often difficult to achieve, particularly in the presence of salts, calcium, solids and other drilling fluid contaminants and/or in the presence of diesel oil.
Uintaite has been treated with certain surfactants to give some water dispersability. Some of these surfactants are themselves very detrimental to drilling mud properties. However, it has been reported that these additives can help minimize hole collapse in geological formations containing water-sensitive, sloughing shales.
The surfactant-coated uintaite powders lose their water-wet characteristics over time and after several circulations in the drilling fluid system. This causes agglomeration and stickiness of the uintaite particles which are then removed by screening thereby eliminating their usefulness in the drilling fluid. Also, the surfactant coating on the uintaite could evaporate or be removed by washing with other additives leaving an undesirable oil-wet uintaite.
Previous attempts have been made to sulfonate uintaite. One such effort is described in U.S. Pat. No. 4,420,405 wherein uintaite is treated with sodium sulfite (Na2SO3) and sodium hydroxide (NaOH) in a mixture with lignite. However, the resultant product did not exhibit the desired water solubility properties of the uintaite portion described above. A need, therefore, exists for a uintaite material that is substantially soluble in water and exhibits some water wet characteristics.
This invention relates to the production of sulfonated uintaite and to well working fluids containing sulfonated uintaite. Sulfonated uintaite is produced, generally, by a controlled sequence of chemical reactions of uintaite, sulfur trioxide, and caustic in either a batch or continuous operation. The product of these reactions is dried, ground and packaged.
More specifically, the process for producing a sulfonated uintaite product according to the present invention is performed according to the following steps:
(a) adding a normally liquid, inert, low boiling point diluent to a charge of uintaite with mixing and agitation to form a mixture of uintaite material and diluent;
(b) contacting the thus formed uintaite/diluent mixture with a liquid or gaseous sulfonating agent under sulfonation conditions to produce sulfonic acids of uintaite;
(c) neutralizing the thus produced sulfonic acids of uintaite with a caustic neutralizing agent under neutralizing conditions to produce sulfonated uintaite;
(d) separating the diluent from the thus produced sulfonated uintaite by evaporation through the use of a heated dryer;
(e) recovering the thus evaporated diluent; and
(f) drying the thus separated sulfonated uintaite as a product of the process.
The product of this process is a sulfonated uintaite which is useful for oil and gas well drilling fluids, oil and gas well completion fluids, and the fluid loss control of hydraulic fracturing fluids for oil and gas wells. This product may also be mixed with known drilling fluids, such as sulfonated asphalt to provide additional benefits. This process may include another embodiment to sulfonate asphalt with added uintaite resulting in a mixture of sulfonated asphalt/sulfonated uintaite. One benefit of adding uintaite during sulfonation is an increase in softening point and thereby faster drying times. A related benefit being the ability to produce sulfonated asphalt at lower levels of sulfonation without the product sticking to the production equipment.
The basic process described above may further include the steps wherein the separated diluent is in a vapor phase while a refrigerant is subjected to alternate compression and expansion in a closed cycle refrigeration system and essentially all of the diluent is further purified and condensed for reuse by passage in indirect heat exchange with the refrigerant.
One object of the present invention is to produce a sulfonated uintaite.
Another object of the invention thus being to provide a method of making uintaite water soluble without adding special surfactants.
A further object of the present invention is to produce the water soluble uintaite material through sulfonation.
Additional objects of the present invention include the preparation of a novel composition of matter having particular utility as a drilling fluid additive and its method of preparation.
A still further object of the present invention is to produce a sulfonated uintaite drilling fluid additive that is highly effective in high salt containing drilling fluid systems, and particularly at elevated downhole temperatures to 300xc2x0 F., or higher.
In accordance with this invention, it is an object to provide a drilling fluid in which sulfonated uintaite provides unexpected improvements in water loss control over other sulfonated products.
Further, an object is to provide a method for dispersing or dissolving uintaite into drilling muds to provide wellbore stability characteristics.
The process of the present invention is capable of producing uintaite at many different levels of sulfonation. In other aspects of the invention, the process provides a method of customizing sulfonated uintaite for use in a wide range of well working fluids including water-based, oil-based, and emulsion types. The process may include in a second embodiment the addition of uintaite to asphalt and sulfonating the mixture. The present invention contemplates these objects as well.
Sulfonated uintaite produced from the present invention may be used in a method of drilling boreholes with drilling fluids wherein the drilling fluid is characterized by desirably low fluid loss in the presence of metal ions and possessing desirable Theological properties.
A better understanding of the invention and its objects and advantages as well as further objects will become apparent to those skilled in this at from the following detailed description, where is described only the preferred embodiment of the invention, simply by way of illustration of the best mode contemplated for carrying out the process of the invention. As will be realized, the invention is capable of modifications in various obvious respects all without departing from the scope of the invention. Accordingly, the detailed description should be regarded as illustrative in nature and not as restrictive.
Preparation of sulfonated uintaite can be carried out using a number of different reactants according to this process. In the preferred embodiment of the invention, sulfonated uintaite is prepared by sulfonating uintaite with a sulfonating agent such as liquid sulfur trioxide, neutralizing the resulting sulfonic acids with a caustic neutralizing agent, and recovering sulfonated uintaite as a product of this process. Suitable sulfonating agents include sulfur trioxide, finning sulfuric acid, chlorosulfonic acid, oleum, and concentrated sulfuric acid. Neutralization of said sulfonic acids with sodium hydroxide or ammonium hydroxide yields water and oil-soluble or dispersible salts of the sulfonated uintaite. Neutralization with Ca(OH)2 (calcium hydroxide) yields a product which is preferable in oil-based muds.
The uintaite can be slurried or dissolved in a suitable diluent (or solvent) such as hexane, heptane, gasoline, kerosene, or the like, prior to reaction with the sulfonating agent. The preferred diluent is an inert, low boiling point liquid. The particularly suitable diluent for this process is n-hexane. It is known that uintaite has limited solubility in hexane. Due to this partial solubility, the term xe2x80x9cdiluentxe2x80x9d is used throughout rather than xe2x80x9csolventxe2x80x9d, however, it is understood that the uintaite may be insoluble, partially soluble, or completely soluble in the diluent. Diluent can be added to the blend at any time during the manufacturing process. The diluent can be separated from the neutralized product by distillation or simple heating during the drying step.
Sulfonated uintaite can be prepared using the above-described process as follows:
a.) A charge of dry, naturally occurring uintaite, is obtained. A colloid mill or other such shearing device may be used to reduce particle size.
b.) The uintaite charge is next augured into a stream of hexane diluent. The mixture includes a 15 to 55% by weight mixture uintaite having a ring and ball softening point in the range of about 300 to 400+ degrees F. with the hexane diluent comprising the balance of the mixture. The mixture is stirred and circulated at room temperature to a maximum of approximately 110xc2x0 F. while low pressure is maintained (to prevent the diluent from volatilizing). The ratios of uintaite and diluent are further set forth in Table I, below.
c.) In a closed, agitated, and stirred vessel, liquid (or gaseous) sulfur trioxide (SO3) is added at a concentration of approximately 23 to 65% by weight of the uintaite to form a reaction product of uintaite. The SO3 is added slowly over approximately 1-3 hours. The significant heat generated by the sulfonation reaction is moderated using heat exchange to maintain a controlled temperature.
d.) Following sulfonation, the reaction product is neutralized with caustic neutralizing agent sodium hydroxide, an alkali metal salt compound, to obtain a pH level between approximately 7 and 9.5 to produce neutralized sulfonated uintaite.
e.) Following neutralization of the sulfonated uintaite, the hexane diluent is removed and the product can be dried. Differing means for drying include conventional rotary dryers, oven dryers, drum dryers, or even with steam stripping followed by drum drying. Due to the high softening point characteristics of the uintaite, drying temperatures can range from 190 to 450 degrees F.
The gaseous by-products of the reaction process are discarded or scrubbed in a known manner. The separated diluent is recycled in a known manner.